Slice Level Reference Picture Reconstruction

ABSTRACT

A method for encoding a video stream, including encoding, by a processor, a first slice of a first picture of the video stream; receiving, from a decoder, a feedback message indicative of having received the first slice of the first picture; and in response to receiving the feedback message indicative of having received the first slice of the first picture, setting the first slice of the first picture as a reference slice for encoding a second picture of the video stream, wherein the second picture is encoded after receiving the feedback message.

TECHNICAL FIELD

This disclosure relates to video coding, and in particular to packet loss resilient video coding using slice-level reference picture reconstruction.

BACKGROUND

Data compression techniques have been developed over the last several decades to reduce the large bandwidth needed by transmission of media (audio, video, or multimedia) data. For example, reference pictures have been used in modern video encoding standards for motion estimation (ME) and motion compensation (MC) to reduce inter-frame redundancy. One side effect of data compression is that the compressed media data is sensitive to data loss or noise, which can happen in best-effort networks. For example, in some cases, network jitter can cause a packet to be lost or overdue for arrival to a decoder, which results in loss of a picture or part of the picture at the decoder. Furthermore, the lost packet can include information to be used (e.g., as part of a reference picture) to decode other pictures, which will cause further harm to the decoding process. As end user devices and network environments become more diversified, reliable media data transmission over noisy networks becomes more challenging.

SUMMARY

Disclosed herein are implementations of methods, apparatuses, and systems for packet loss resilient video coding using slice-level reference picture reconstruction.

In one aspect, a method for encoding a video stream is disclosed. The method includes encoding, by a processor, a first slice of a first picture of the video stream; receiving, from a decoder, a feedback message indicative of having received the first slice of the first picture; and in response to receiving the feedback message indicative of having received the first slice of the first picture, setting the first slice of the first picture as a reference slice for encoding a second picture of the video stream, wherein the second picture is encoded after receiving the feedback message.

In another aspect, a method for decoding an encoded video stream is disclosed. The method includes receiving, from an encoder, data associated with a first slice of a first picture of the encoded video stream; based on a determination that all data required for decoding the first slice of the first picture has been received, sending, to the encoder, a feedback message indicative of having received the first slice of the first picture, and decoding, by a processor, the first slice of the first picture; receiving, from the encoder, data associated with a first slice of a second picture of the encoded video stream with reference to the first slice of the first picture; and setting the first slice of the first picture as a reference slice for decoding the second picture of the encoded video stream.

In another aspect, an apparatus for decoding an encoded video stream is disclosed. The apparatus includes a non-transitory memory and a processor, wherein the non-transitory memory includes instructions executable by the processor to receive, from an encoder, data associated with a first slice of a first picture of the encoded video stream; based on a determination that all data required for decoding the first slice of the first picture has been received, send, to the encoder, a feedback message indicative of having received the first slice of the first picture, and decode, by a processor, the first slice of the first picture; and receive, from the encoder, data associated with a first slice of a second picture of the encoded video stream with reference to the first slice of the first picture; and set the first slice of the first picture as a reference slice for decoding the second picture of the encoded video stream.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to-scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity.

FIG. 1 is a diagram of an example system for media data transmission according to implementations of this disclosure.

FIG. 2 is a diagram of example structures of a video stream.

FIG. 3 is a diagram of an example encoding process according to implementations of this disclosure.

FIG. 4 is a diagram of an example decoding process according to implementations of this disclosure.

FIG. 5 is a flowchart of an example process for decoding an encoded video stream using slice-level reference picture reconstruction according to implementations of this disclosure.

FIG. 6 is a flowchart of an example process for encoding a video stream using slice-level reference picture reconstruction according to implementations of this disclosure.

FIGS. 7A, 7B, 7C and 7D are examples of slice-level reference picture reconstruction according to implementations of this disclosure.

FIG. 8 is another example of slice-level reference picture reconstruction according to implementations of this disclosure.

DETAILED DESCRIPTION

Online multimedia data sharing, such as a video conference call, a live-stream video broadcasting, or an Internet phone service, requires media data transmission with efficiency and fidelity. The media data can include audio data, video data, or any multimedia data including an audio sequence or a video sequence. Typically, media data can be stored in its original form or converted to form a video stream. The video stream can be encoded (or “compressed”) into a compressed video stream (e.g., a video bitstream) for transmission over a network. The compressed video stream can be transmitted over a network in data packets (or “packets” for simplicity).

When encoding the video stream (also referred to as a “video sequence”), a picture of the video stream can be encoded using motion estimation (ME) and motion compensation (MC). For example, a picture can be decoded using another picture as a reference (referred to as a “reference picture”). The reference picture can be an I-picture (a picture coded without referencing another picture), or a P-picture (a picture coded using another picture as a reference). During encoding and decoding, the picture can be divided or segmented into one or more slices. In some instances, ME and MC can be performed within each slice without relying on other slices in the same picture. As a result, when a slice is lost, other slices in the same picture are not affected. A slice can include one or more blocks.

According to implementations of this disclosure, a decoder receives a slice from a picture, and sends a feedback message to an encoder indicating that the slice has been received. When the feedback message arrives at the encoder, the encoder sets the slice as a reference slice, so that it can be used for encoding slices in subsequent pictures. It will take some time for the feedback message to arrive, especially when the network condition is jittery. Before receiving the feedback message, without knowing whether the slice has safely arrived at the decoder, the encoder will not use it as reference. After receiving the feedback message, the encoder can start using the slice as reference for encoding a new slice in a new picture and indicate this reference information in the slice header of the new slice. Upon receiving the new slice, the decoder can tell from the slice header that the slice, which was received and acknowledged by the decoder in the feedback message, is going to be used as a reference slice for decoding the new slice.

The slices to be predicted from the reference slices can be co-located slices, e.g., some areas of the slices from the same location in the picture that often do not incur much change from picture to picture. In some implementations, pictures including valid reference slices can be set as long-term reference pictures (LTRs). The LTRs will be updated when a new slice from a new picture is received.

A slice can be included in one packet or divided into multiple packets. By using slice-level feedback messages to update reference slices used for encoding slices (such as co-located slices) of subsequent pictures, and without requiring that the whole picture to be received, the slice-level reference picture reconstruction can increase packet loss resilience under jittery network conditions. The slice-level reference picture reconstruction techniques described in this disclosure can introduce a noticeable improvement in performance, bits savings, and mitigating effects on packet loss. For example, even when only one slice is received for a certain picture, that slice can still be used as a reference slice. In addition, the slice-level reference picture reconstruction techniques can be integrated or made compliant with existing video standards, such as, for example, H.264 and HEVC.

It should be noted that the applications and implementations of this disclosure are not limited to the examples, and alternations, variations, or modifications of the implementations of this disclosure can be achieved for any computation environment. Details of the disclosed methods, apparatus, and systems will be set forth below after an overview of the system and coding structures.

FIG. 1 is a diagram of an example system 100 for media data transmission according to implementations of this disclosure. As discussed above, the media data can include audio data, video data, or any multimedia data including an audio sequence or a video sequence. As shown in FIG. 1, the system 100 can include multiple apparatuses and networks, such as an apparatus 102, an apparatus 104, and a network 106. The apparatuses can be implemented by any configuration of one or more computers, such as a microcomputer, a mainframe computer, a supercomputer, a general-purpose computer, a special-purpose/dedicated computer, an integrated computer, a database computer, a remote server computer, a personal computer, a laptop computer, a tablet computer, a cell phone, a personal data assistant (PDA), a wearable computing device, or a computing service provided by a computing service provider, for example, a web host or a cloud service provider. In some implementations, the computing device can be implemented in the form of multiple groups of computers that are at different geographic locations and can communicate with one another, such as by way of a network. While certain operations can be shared by multiple computers, in some implementations, different computers are assigned to different operations. In some implementations, the system 100 can be implemented using general-purpose computers/processors with a computer program that, when executed, carries out any of the respective methods, algorithms, and/or instructions described herein. In addition, or alternatively, for example, special-purpose computers/processors including specialized hardware can be utilized for carrying out any of the methods, algorithms, or instructions described herein.

The apparatus 102 can have an internal configuration of hardware including a processor 108 and a memory 110. The processor 108 can be any type of device or devices capable of manipulating or processing information. In some implementations, the processor 108 can include a central processor (e.g., a central processing unit or CPU). In some implementations, the processor 108 can include a graphics processor (e.g., a graphics processing unit or GPU). In some implementations, the processor 108 can include a special dedicated hardware accelerating processor. Although the examples herein can be practiced with a single processor as shown, advantages in speed and efficiency can be achieved using more than one processor. For example, the processor 108 can be distributed across multiple machines or devices (each machine or device having one or more processors) that can be coupled directly or connected via a network (e.g., a local area network). The memory 110 can include any transitory or non-transitory device or devices capable of storing codes and data that can be accessed by the processor (e.g., via a bus). The memory 110 herein can be a random-access memory (RAM) device, a read-only memory (ROM) device, an optical/magnetic disc, a hard drive, a solid-state drive, a flash drive, a security digital (SD) card, a memory stick, a compact flash (CF) card, or any combination of any suitable type of storage device. In some implementations, the memory 110 can be distributed across multiple machines or devices, such as in the case of a network-based memory or cloud-based memory. The memory 110 can include data, an operating system and applications. The data can include any data for processing (e.g., an audio stream, a video stream, or a multimedia stream). The applications can include programs that permit the processor 108 to implement instructions to generate control signals for performing functions of the methods in the following description.

In some implementations, in addition to the processor 108 and the memory 110, the apparatus 102 can also include a secondary (e.g., external) storage device (not shown). When present, the secondary storage device can provide additional memory when high processing needs exist. The secondary storage device can be a storage device in the form of any suitable non-transitory computer-readable medium, such as a memory card, a hard disk drive, a solid-state drive, a flash drive, or an optical drive. Further, the secondary storage device can be a component of the apparatus 102 or can be a shared device accessible via a network. In some implementations, the application in the memory 110 can be stored in whole or in part in the secondary storage device and loaded into the memory 110 as needed for processing.

In addition to the processor 108 and the memory 110, the apparatus 102 can include input/output (I/O) devices. For example, the apparatus 102 can include an I/O device 112. The I/O device 112 can be implemented in various ways, for example, it can be a display that can be coupled to the apparatus 102 and configured to display a rendering of graphics data. The I/O device 112 can be any device capable of transmitting a visual, acoustic, or tactile signal to a user, such as a display, a touch-sensitive device (e.g., a touchscreen), a speaker, an earphone, a light-emitting diode (LED) indicator, or a vibration motor. The I/O device 112 can also be any type of input device either requiring or not requiring user intervention, such as a keyboard, a numerical keypad, a mouse, a trackball, a microphone, a touch-sensitive device (e.g., a touchscreen), a sensor, or a gesture-sensitive input device. If the I/O device 112 is a display, for example, it can be a liquid crystal display (LCD), a cathode-ray tube (CRT), or any other output device capable of providing a visible output to an individual. In some cases, an output device can also function as an input device—a touchscreen display configured to receive touch-based input, for example.

The I/O device 112 can alternatively or additionally be formed of a communication device for transmitting signals and/or data. For example, the I/O device 112 can include a wired means for transmitting signals or data from the apparatus 102 to another device. For another example, the I/O device 112 can include a wireless transmitter or receiver using a protocol compatible to transmit signals from the apparatus 102 to another device or to receive signals from another device to the apparatus 102.

In addition to the processor 108 and the memory 110, the apparatus 102 can optionally include a communication device 114 to communicate with another device. Optionally, the communication can be via a network 106. The network 106 can be one or more communications networks of any suitable type in any combination, including, but not limited to, networks using Bluetooth communications, infrared communications, near field connections (NFCs), wireless networks, wired networks, local area networks (LANs), wide area networks (WANs), virtual private networks (VPNs), cellular data networks, or the Internet. The communication device 114 can be implemented in various ways, such as a transponder/transceiver device, a modem, a router, a gateway, a circuit, a chip, a wired network adapter, a wireless network adapter, a Bluetooth adapter, an infrared adapter, an NFC adapter, a cellular network chip, or any suitable type of device in any combination that is coupled to the apparatus 102 to provide functions of communication with the network 106.

Similar to the apparatus 102, the apparatus 104 includes a processor 116, a memory 118, an I/O device 120, and a communication device 122. The implementations of elements 116-122 of the apparatus 104 can be similar to the corresponding elements 108-114 of the apparatus 102. For example, the apparatus 102 can be used as a decoding apparatus (referred to as a “decoder”), and the apparatus 104 can be used as an encoding device (referred to as an “encoder”), or vice versa. The apparatus 102 can communicate with the apparatus 104 via the network 106. The apparatuses 102 and 104 can also communicate with other apparatuses (not shown) connected to the network 106. It should be noted that parts or components of the coding devices (e.g., apparatuses 102 and 104) and systems can include elements not limited to those shown in FIG. 1, and can include more or fewer parts, components, and hardware or software modules for performing various functions in addition or related to encoding and decoding using slice-level reference picture reconstruction.

The apparatuses 102 and 104 (and any algorithms, methods, instructions, etc., stored thereon and/or executed thereby) can be realized in hardware including, for example, intellectual property (IP) cores, application-specific integrated circuits (ASICs), programmable logic arrays, optical processors, programmable logic controllers, microcode, firmware, microcontrollers, servers, microprocessors, digital signal processors, or any other suitable circuit. In this disclosure, the term “processor” should be understood as encompassing any the foregoing, either singly or in combination. The terms “signal,” “data,” and “information” are used interchangeably. Further, portions of the apparatuses 102 and 104 do not necessarily have to be implemented in the same manner.

It should be noted that parts or components of the coding devices implementing the slice-level reference picture reconstruction (e.g., apparatuses 102 and 104) and systems can include elements not limited to those shown in FIG. 1. Without departing from the scope of this disclosure, the coding devices and systems can include more or fewer parts, components, and hardware or software modules for performing various functions in addition or related to encoding and decoding.

FIG. 2 shows example pictures of a video stream 200. The video stream 200 can include a series of pictures along the timeline, including pictures 202-208. For example, the picture 208 can be the current picture in the coding process. The reference pictures for the picture 208 as can be one or more of the pictures 206, 204, 202, or another picture (not shown) coded before the picture 208.

Each picture of the video stream 200 can be divided into multiple processing units. In some video coding standards, the processing units are referred to as “macroblocks” or “coding tree blocks” (CTBs). In some implementations, each processing unit can be further divided into one or more processing sub-units, in which the processing sub-units are referred to as “blocks” or “coding units” (CUs). The size and shape of the processing units and sub-units can be any size, such as 8×8, 8×16, 16×16, 32×32, 64×64, or any arbitrary shape. Typically, when a region has more details, the processing units and sub-units tend to be smaller in size. For ease of explanation without causing ambiguity, the processing units and sub-units are referred to as “blocks” hereinafter unless explicitly described otherwise. For example, in FIG. 2, the picture 206 is shown to have 16×16 blocks, including a block 210. The boundaries of the blocks are shown in dotted lines.

In some implementations, the blocks can be grouped, forming a special region or partition of the picture. In other words, the picture can be divided into one or more regions or partitions, and each region or partition can include one or more blocks. Such regions or partitions can be referred to as “slices,” “tiles,” or another name specific to certain video coding standards. For ease of explanation without causing ambiguity, such regions or partitions are referred to as “slices” hereinafter unless explicitly described otherwise herein. For example, the picture 206 can be divided into four slices 212-218, each slice having four blocks. The slices 212-218 can have boundaries 220-226 in between, shown as solid lines.

Slices can be processed independently of other slices. For example, motion compensation and/or motion estimation can be performed for one slice (e.g., using blocks in the same slice). In addition, slices can be encoded simultaneously with and/or independently from the other slices. For example, the slices 212-218 can be independently processed, which can increase the efficiency of video encoding. Similarly, the slices can also be independently decoded at a decoder.

Slices of an I-picture can be referred to as I-slices, and slices of a P-picture can be referred to as P-slices. For P-slices, ME and/or MC can be performed between two or more co-located slices in some implementations. As used herein, the term “co-located” refers to two slices in two respective pictures having the same location in the picture. The location of a slice in a picture refers to the relative position of the slice within the picture. The location can be determined using a part of the slice as a reference point. For example, the reference point can be within a block of the slice at the center, a corner, a boundary, or any position of the slice. In some instances, two co-located slices can have the same size and the same shape. For example, for two slices in two pictures having the same size and shape, if the top left corners of the two slices have the same positions (e.g., coordinates) in the picture, the two slices are considered “co-located.” For example, the slice 228 of the picture 208 is co-located with the slice 212 of the picture 206, and so on. If the slice 228 is a P-slice, it can use the co-located slice 212 as its reference slice. In some other implementations, for P-slices, ME and/or MC can be performed between two or more non-co-located slices. For example, if the slice 228 is a P-slice, it can use the non-co-located slice 214,216, or 218 as its reference slice.

It should be noted that the slice herein can include any number of any blocks in any configuration, and is not limited to the aforementioned examples (e.g., the slices 212-218). For example, a slice can be in a rectangular shape, such as including blocks of adjacent rows. In another example, a slice can include blocks grouped in a non-contiguous manner, such as two or more non-contiguous block groups. In another example, a part of a first slice can be within a part of a second slice. In yet another example, the first slice can be enclosed by the second slice (e.g., the first slice can be within the second slice).

It should also be noted that the division or segmentation of the slices can be changed or unchanged in the video stream. In other words, the boundaries between the slices can be changed or unchanged. In some implementations, the pictures of the video stream can be divided into slices in the same pattern. In some implementations, the pattern of the slices can change from picture to picture in the video stream.

FIG. 3 is a flowchart of an example process 300 of encoding a video stream 302 according to implementations of this disclosure. The video stream 302 can include an audio source stream, a video source stream, or any media stream including audio and/or video data. The process 300 can be implemented as software and/or hardware modules in the system 100 in FIG. 1. For example, the process 300 can be implemented as modules included in an encoder (e.g., the apparatus 104 in FIG. 1). The process 300 includes operations 304-308 to produce as output a compressed video stream 314 from a video stream 302. The example encoding process 300 (either the whole process or some stages) can be further modified when implementing slice-level reference picture reconstruction described below in FIGS. 5 and 6. In some instances, process 300 may not be necessary for the implementations of slice-level reference picture reconstruction.

Referring to the process 300 in FIG. 3, the video stream 302 is received by an encoder. The term “receive” used herein can refer to receiving, inputting, acquiring, retrieving, obtaining, reading, accessing, or any action in any manner for inputting information or data. For example, the video stream 302 can be a video stream and include a series of video pictures (e.g., a current picture).

Generally, an encoding process can include one or more of the following stages or operations: a prediction stage (e.g., for intra-prediction or inter-prediction), a transformation stage (with or without quantization), and an entropy encoding stage. The aforementioned stages can be used to output the compressed video stream 314 from the video stream 302 in a forward path of the encoding process as shown by the solid connection lines in FIG. 3: an intra/inter prediction stage 304, a transformation and/or quantization stage 306, and an entropy encoding stage 308.

At the intra/inter prediction stage 304, for intra-prediction, a current block of the current picture can be predicted using previously coded block(s) from the current picture. For inter-prediction, the current block of the current picture can be predicted using previously coded pictures as reference data. Previously coded pictures can include, for example, previously encoded and reconstructed pictures also referred to as reference pictures. For example, motion estimation and compensation can be performed using the current picture and one or more reference pictures to generate motion data. A residual, which is the difference between a predicted block and the current block, can be further transformed, quantized, and/or entropy encoded.

In some implementations, optionally, a loop filter (not shown) can be additionally applied before the entropy encoding stage 308. The loop filter can reduce distortion (e.g., blocking artifacts) introduced by the video compression. Other information used to decode the resulted video bitstream can also be entropy encoded, such as the prediction mode, transformation type, quantization level, and loop filter parameters (e.g., filter strength).

In some implementations, the process 300 can further include a reconstruction path for reconstructing reference data to be used for predicting a future picture. For example, the reconstruction path (shown by the dotted connection lines in FIG. 3) can include the following stages: a dequantization and/or inverse transformation stage 310 and a reconstruction stage 312. The stages 310 and 312 can be used to ensure that both the encoder (e.g., the apparatus 104 in FIG. 1) and a decoder (e.g., the apparatus 102 in FIG. 1) can use the same reference data for prediction. In some implementations, optionally, a loop filter (not shown) can be additionally applied after the stage 312. In other implementations, the reconstructed picture can be used without using the loop filter. The reconstruction can be similar to a reconstruction stage in a decoding process (e.g., stage 410 in FIG. 4).

It should be noted that other variations of the encoding process can be used to encode the video sequence. The encoding process can be performed in different orders, combined into fewer stages, and/or divided into more stages. For example, quantization or transform can be optional in some implementations. As an example, a non-transform based encoder can quantize the residual data without transformation.

FIG. 4 is a diagram of an example process 400 that can be used to decode a compressed video stream according to implementations of this disclosure. The process 400 can be implemented as software and/or hardware modules in the system 100 in FIG. 1. For example, some or all stages of the process 400 can be implemented as software or hardware modules included in the system 100 by a decoder (e.g., the apparatus 102). The decoder can be implemented by program codes stored in memory (e.g., the memory 110). The program codes can include computer-readable instructions that, when executed by a processor (e.g., the processor 108), cause the decoder to decode a compressed video stream in the manner described in FIG. 4. The decoder can also be implemented as specialized hardware included in an apparatus (e.g., the apparatus 102). For example, the decoder can be a hardware decoder. The process 400 includes operations 404-410 to reconstruct a video stream 412 from a compressed video stream 402. In addition, the example process 400 (either the whole process or some stages) can be modified when implementing slice-level reference picture reconstruction of FIGS. 5-6 described below.

Generally, when decoding a compressed media stream, the decoding process is similar to the reconstruction path of the video encoding process. The process 400, similar to the reconstruction path of the process 300 discussed above, can include the following stages: an entropy decoding stage 404, a dequantization and/or inverse transformation stage 406, an intra/inter prediction stage 408, and a reconstruction stage 410. The reconstructed picture can be used as future reference data for processing a future picture successive to the current picture. In addition to be outputted in the media stream 412, the reconstructed picture can also be stored in a buffer (e.g., in the memory 110 in FIG. 1) to be used as the future reference data. In some implementations, the reconstructed picture can be filtered using a loop filter (not shown). Other structural variations of the process 400 can be used to decode the compressed video stream 402.

FIG. 5 is a flowchart of an example process 500 for encoding a video stream using slice-level reference picture reconstruction according to implementations of this disclosure. The process 500 can be implemented as software and/or hardware modules in the system 100 in FIG. 1. For example, the process 500 can be implemented as software modules stored in the memory 118 as instructions and/or data executable by the processor 116 of an encoder, such as the apparatus 104 in FIG. 1. In another example, the process 500 can be implemented in hardware as a specialized chip storing instructions executable by the specialized chip. Some or all of the operations of the process 500 can be implemented at one or more stages of the process 300 in FIG. 3.

At an operation 502, a first slice of a first picture of the video stream is encoded. The encoded slice is transmitted in the compressed video stream and received by a decoder, such as the apparatus 102 in FIG. 1. For example, the first slice can be associated with a slice number and will be referred to herein with the slice number (e.g., a slice “S0”, shown in FIG. 7A as a slice 712, herein referenced as slice “S0” 712) along with the picture that the slice belongs to (e.g., a picture 702).

Based on a determination that all data required for decoding the first slice of the first picture has been received, the decoder sends a feedback message indicative of having received the first slice of the first picture to the encoder, the process of which will be discussed in detail below in FIG. 6. Using FIG. 7A as an example, slice “S0” 712 of a picture 702 is encoded and transmitted in the compressed video stream (“bitstream”). When the slice “S0” 712 is received by the decoder, the decoder sends a feedback message to the encoder indicative of having received slice “S0” 712 of the picture 702.

At an operation 504, a feedback message indicative of having received the first slice of the first picture is received from the decoder. In the example of FIG. 7A, the feedback message can be, for example, the feedback message indicative of having received slice “S0” 712 of the picture 702.

At an operation 506, in response to receiving the feedback message indicative of having received the first slice of the first picture, the first slice of the first picture is set as a reference slice. The reference slice can be used for encoding a second picture of the video stream, which is encoded later in time than the first picture. In the example of FIG. 7A, in response to receiving the feedback message indicative of having received slice “S0” 712 of the picture 702, the slice “S0” of the picture 702 is set as a reference slice, which can be used for encoding subsequent pictures, such as a picture 704 in FIG. 7B.

Meanwhile, based on a determination that the first picture has not been set as a reference picture and in response to receiving the feedback message, the first picture is set as a new reference picture for encoding the second picture of the video stream. This can be done concurrently, subsequently, or prior to the operation 506. For example, both the encoder and decoder can set a set of reference pictures used for predicting the second picture. The set of reference picture can be set to include each picture that is associated with at least one valid reference slice. In some implementations, the set of reference pictures used for predicting the second picture further includes a fourth picture encoded immediately prior to encoding the second picture (e.g., “last” picture). For example, the fourth picture can be encoded and then decoded using the reconstruction path in FIG. 3 so that the encoder and decoder can use the same reference picture reconstructed from the encoded video stream. Referring to FIG. 7B as an example, when a feedback message regarding a slice “S0” 718 of the picture 704 is received, the picture 704 can be set as a new reference picture, and the set of reference pictures after receiving the feedback message regarding slice “S0” 718 of the picture 704 can include, for example, the picture 702 and the picture 704, each including at least one valid reference slice.

In some implementations, such as ones using long-term reference (LTR) pictures, the first picture can be set as a new LTR picture. In the example of FIG. 7A, the picture 702 can be set as a new LTR picture for encoding subsequent pictures.

In some implementations, the first slice of the first picture can be set as a valid reference slice. A corresponding slice of another picture, which was previously valid, can be set as an invalid reference slice. More specifically, in response to setting the first slice of the first picture as the reference slice for encoding the second picture of the video stream, a first slice of a third picture of the video stream can be as an invalid reference slice, wherein the first slice of the first picture and the first slice of the third picture are co-located, and the third picture was encoded prior to encoding the first picture. Using FIG. 7B as an example, when a slice “S0” 718 of the picture 704 is set as a valid reference slice, the previously valid slice “S0” 712 of the picture 702 is set as invalid.

Subsequently, a first slice of the second picture of the video stream can be encoded with reference to the first slice of the first picture, wherein the first slice of the first picture and the first slice of the second picture are co-located. For example, a slice header of the first slice of the second picture can include reference to the first slice of the first picture, which is used for predicting the first slice of the second picture during decoding. For example, in FIG. 7B, a slice “S1” of the picture 704 can be encoded with reference to the slice “S1” 714 of the picture 702. The slice “S1” of the picture 704 is co-located with the slice “S1” 714 of the picture 702.

In some implementations, a second feedback message indicative of having received a second slice of the first picture is received from the decoder, wherein the second slice of the first picture is not the same as the first slice of the first picture. This occurs when multiple slices from the same picture are received by the decoder and multiple feedback messages are sent by the decoder. As a result, in response to receiving the second feedback message, the encoder sets the second slice of the first picture as a reference slice for encoding the second picture of the video stream, and both the first slice and the second slice of the first picture are set as valid reference slices.

In some other implementations, the feedback message is indicative of having received the first slice and at least one other slice of the first picture. This occurs when multiple slices from the same picture are received by the decoder and one feedback message acknowledging all received slices are sent by the decoder. This will lower transmission and processing costs, but will increase the latency for updating the reference slices/pictures, as the decoder will have to wait longer for all the slices to arrive before sending the feedback message.

FIG. 6 is a flowchart of an example process 600 of decoding a compressed video stream using slice-level reference picture reconstruction according to implementations of this disclosure. The compressed video stream can be received in the format of a video bitstream. The process 600 can be implemented as software and/or hardware modules in the system 100 in FIG. 1. For example, the process 600 can be implemented as modules included in a decoder (e.g., the apparatus 102 in FIG. 1). The operations of the process 600 can also be implemented as machine-readable instructions at, for example, at one or more stages of the process 400 in FIG. 4. The process 600 includes operations 602-608 for slice-level reference picture reconstruction from the received video stream, which are set forth as follows.

At an operation 602, data associated with a first slice of a first picture of the encoded video stream is received from an encoder. For example, using FIG. 7A as an example, data associated with the slice “S0” 712 of a picture 702 is received from the encoder.

At an operation 604, based on a determination that all data required for decoding the first slice of the first picture has been received, a feedback message indicative of having received the first slice of the first picture is sent to the encoder. In the example of FIG. 7A, upon determining that all data required for decoding the slice “S0” 712 has been received, the decoder sends a feedback message to the encoder indicative of having received slice “S0” 712 of the picture 702. For example, the slice can arrive in one packet or multiple packets.

Besides sending the feedback message, the decoder decodes the first slice of the first picture based on the received data. For example, the slice “S0” 712 of the picture 702 can be decoded. A slice can be decoded using reference to other pictures, such as the set of reference pictures discussed above. For example, the slice “S0” 712 of the picture 702 can be decoded using previously decoded reference pictures. In some implementations, the reference pictures can also include the “last” picture in the sequence decoded immediately prior to decoding the first picture.

At an operation 606, data associated with a first slice of a second picture of the encoded video stream with reference to the first slice of the first picture is received from the encoder. For example, a slice header of the first slice of the second picture can include reference to the first slice of the first picture, wherein the first slice of the first picture is used for predicting the first slice of the second picture during decoding.

At an operation 608, the decoded first slice of the first picture is set as a reference slice for decoding the first slice of the second picture of the encoded video stream. The first slice of the first picture and the first slice of the second picture can be co-located. For example, in FIG. 7B, slice “S0” 718 of the picture 704 can be decoded using the co-located slice “S0” 712 of the picture 702, which is set as a reference slice in FIG. 7A.

Next, the first slice of the second picture of the video stream can be decoded with reference to the first slice of the first picture. For example, the first slice of the second picture can be decoded using the first slice of the first picture as reference, based on information included in the slice header of the first slice of the second picture.

Without repeating every detail, the reference slices and pictures can be updated similar to the process 500 in FIG. 5. For example, in some implementations, such as ones using long-term reference (LTR) pictures discussed above, the first picture can be set as a new LTR picture. In the example of FIG. 7A, the picture 702 can be set as a new LTR picture for decoding subsequent pictures, when the slice header indicates using the picture 702 as a reference picture. In some implementations, based on a determination that the first picture has not been set as a reference picture and in response to receiving, from the encoder, data associated with the first slice of the second picture with reference to the first slice of the first picture, the first picture can be set as a new reference picture for decoding the second picture. In some implementations, the first slice of the first picture can be set as a valid reference slice.

In some implementations, based on a determination that all data required for decoding a second slice of the first picture has been received, a second feedback message indicative of having received the second slice of the first picture can be sent to the encoder, and the second slice of the first picture can be decoded, wherein the second slice of the first picture is not the same as the first slice of the first picture. Data associated with a second slice of the second picture of the encoded video stream with reference to the second slice of the first picture is received from the encoder. The second slice of the first picture is set as a reference slice for decoding the second picture, wherein both the first slice and the second slice of the first picture are set as valid reference slices.

In some implementations, in response to setting the first slice of the first picture as the reference slice for decoding the second picture of the video stream, a first slice of a third picture of the video stream is set as an invalid reference slice. The first slice of the first picture and the first slice of the third picture are co-located, and the third picture is decoded prior to decoding the first picture.

In some implementations, the feedback message is indicative of having received the first slice and at least one other slice of the first picture. In some other implementations, as soon as receiving a slice, a feedback message is sent.

FIGS. 7A, 7B, 7C and 7D are examples of slice-level reference picture reconstruction according to implementations of this disclosure. In these examples, each picture is divided into slices labeled as “S0”, “S1”, “S2”. For ease of explanation, a slice labeled “S0” corresponds to the first slice discussed above in the processes 500 and 600, a slice labeled “S1” corresponds to the second slice discussed above, and a slice labeled “S2” corresponds to the third slice discussed above, and so on.

Slices with the same labels are co-located. For example, slices labeled “S0” are co-located. Similarly, slices labeled “S2” are co-located. As previously discussed, the slice “S0” 712 of picture 702 and the slice “S0” 718 of picture 704 are co-located. Likewise, slice “S2” 716 of the picture 702 and slice “S2” 720 of the picture 706 are co-located.

When packets containing one or more slices are received by the decoder, a picture (e.g., the picture 702) becomes decodable (e.g., partially or fully decodable). For example, in FIG. 7A, when the packets containing all slices in the picture are received by the decoder, a feedback message (or multiple feedback messages) indicating that all the slices (in this example, slice “S0” 712, slice “S1” 714 and slice “S2” 716) are received is sent by the decoder back to the encoder over the network. There can be some transmitting delay. When the encoder receives the feedback message(s), the picture (e.g., the picture 702) is marked as a long-term reference picture, e.g., LTR0. The slices (“S0”, “S1”, “S2”) are made valid for ME and MC, and can be used as reference in subsequent coding process. In this example, the picture 702 becomes LTR0 with all slices set as valid.

Back to the decoding process, in FIG. 7B, a new slice “S0” 718 of a newer picture, the picture 704, is received. A (second) feedback message indicating that the slice “S0” 718 of the picture 704 has been received is sent back to the encoder. When the encoder receives the feedback message, the newer picture, e.g., the picture 704, is marked as a long-term reference picture, e.g., LTR1, which can be used as reference in subsequent encoding process, together with the previous long-term reference pictures that are still valid. In this example, the picture 704, which includes the received slice “S0” 718, is set as LTR1. At this time, the slices 714, 716 {“S1”, “S2”} of LTR0 are still valid, but the slice “S0” 712 in LTR0 becomes invalid. As a result, future ME and MC is restricted to use references within the valid slices in LTR0 and LTR1, which are {“S1”, “S2”} of the picture 702 and {“S0”} of the picture 704.

Next, in FIG. 7C, another slice, e.g., slice “S2” 720 of a newer picture 706, is received. Another feedback message is sent back to the encoder. When the encoder receives the feedback message, the corresponding picture, e.g., the picture 706, is set as a valid long-term reference picture LTR2. The received slice “S2” 720 is set a valid reference slice. At this time, only the slice “S1” 714 of LTR0 and the slice “S0” 718 of LTR1 remain valid (which means the slice “S2” 716 of LTR0 is set as invalid). Similarly, future ME and MC is restricted to use references within the valid reference slices in LTR0, LTR1 and LTR2. In this example, the valid reference slices are the slice “S1” 714 of the picture 702, the slice “S0” 718 of the picture 704 and the slice “S2” 720 of the picture 706.

In some implementations, when multiple slices of the same picture are received, the process can proceed as shown in another example in FIG. 7D. In FIG. 7D, the first two pictures are received in the same way as the examples in FIGS. 7A-B. Next, when both the slice “S0” 722 and the slice “S2” 720 of the picture 706 are received in the decoding process, a feedback message indicating that both the slice “S0” 722 and the slice “S2” 720 are received is sent back to the encoder. When the encoder receives the feedback message, the picture 706 can be set as a long-term reference picture, which can be used as a reference in subsequent encoding process, together with previous long-term reference pictures that are still valid. In this example, the picture 706 is set as LTR2 with slices 722, 720 {“S0”, “S2”}. At this time, the slice “S1” 714 of the picture 702 is still valid, but the slice “S0” of the picture 704 is set as invalid, because the newer “S0”, the slice 722, has become available in LTR2. As a result, future ME and MC of a slice is restricted to use references within the valid slices in LTR0, LTR1 and LTR2 (LTR1 including no valid slice). In some implementations, a long-term reference picture with no valid reference slice can be replaced with a newer long-term reference picture, when the newer picture contains at least one valid reference slice.

FIG. 8 is another example of slice-level reference picture reconstruction according to implementations of this disclosure. In this example, the process is shown in a timing point of view from left to right.

At a decoder 850, after decoding picture Pi, the picture Pi and long-term reference pictures {LTRi}c 852 can be used as references. The corresponding long-term reference pictures at an encoder 800 are shown as {LTRi}c 802. Assume that the first slice received after the picture Pi, denoted as slice K, belongs to a picture P(i+T) with T>=1. In this example, T=1, which means that the slice K belongs to picture P(i+1). The slice K is decoded by the current reference pictures, including the long-term reference pictures {LTRi}c 852 and optionally the “last” picture discussed above. Meanwhile, a feedback message signaling “slice K is received” is sent to the encoder 800. Depending on the network condition, it can take some time for the feedback message to arrive at the encoder 800.

The feedback message arrives the encoder 800, for example, during encoding of a picture P(i+N), which occurs later in time than P(i+T). In this example, the feedback message arrives during encoding of a picture P(i+4) with N=4, which occurs later in time than the picture (i+1). Upon arrival of the feedback message, the long-term reference pictures can be updated to include the picture P(i+T). In this example, T=1. The updated long-term reference pictures {LTRi}n 804 can be used as references for encoding a future picture, such as picture P(i+N+1). In this example (N=4), {LTRi}n 804 can be used as references starting from a new picture P(i+5).

As discussed above, information of the reference picture(s) can be carried in the slice header. For example, the slice header can be fully or partially compliant with some video standards, such as, for example, H.264 and HEVC. The reference information can also be processed or encoded in other ways, and not necessarily be made to be compliant with any existing standards.

When a slice in the new picture P(i+5) is encoded with the picture P(i+1) in the {LTRi}n 804 as a reference picture, such information can be carried in the slice header. Upon receiving information in the slice header indicating that the picture P(i+1) is used as reference, the long-term reference pictures {LTRi}c 852 at the decoder 850 can be updated to include the picture P(i+1). The updated long-term reference pictures {LTRi}n 854 can be used as references to decode slices in pictures starting from P(i+N+1), e.g., picture P(i+5) in the illustrative example.

In some implementations, such as when only the long-term reference pictures are used as references, any lost slices, such as slices in the pictures P(i+2), P(i+3) or P(i+4), will not affect the decoding of the next picture P(i+5). The decoder will recover from packet loss of slices in P(i+2), P(i+3) or P(i+4).

In some implementations, instead of sending the feedback message right away when a slice is received, the decoder 850 can wait (subject to certain latency limit) until all slices have been received for a certain picture before sending the feedback message. This can mean more delay as the slices would not arrive at the same time. On the other hand, fewer feedback messages are sent (only one per picture), which lowers the transmission and processing cost.

In some implementations, more than one decoder corresponds to one encoder, e.g., in a multicast scenario. The encoder can determine whether feedback messages have been received for a common slice from all of the decoders. If so, the LTRs can be updated. The information of the common slice can be carried in the slice header, such as one that is compliant with certain video standards. For example, when the packet loss rate is 10%, for a 1:4 multicast (one encoder, four decoders), the probability of a slice being received by all four decoders is 66%. When the packet loss rate drops to 20%, the probability drops to 41%. In another example, for a 1:16 multicast (one encoder, sixteen decoders), the probability of a slice being received by all sixteen decoders is 19% when the packet loss rate is 10%, and 2.8% when the packet loss rate is 20%.

Furthermore, when some decoders are broken, such as when all packets of some key pictures are lost, the processes described above can be carried out in the other decoders that are still running. Meanwhile, the broken decoders can be recovered when a new immediate direct fresh (IDR) picture is received.

As described above, a person skilled in the art should be noted that, all or a portion of aspects of the disclosure described herein can be implemented using a general purpose computer/processor with a computer program that, when executed, carries out any of the respective techniques, algorithms and/or instructions described herein. In addition, or alternatively, for example, a special purpose computer/processor can be utilized which can contain specialized hardware for carrying out any of the techniques, algorithms, or instructions described herein.

The implementations of computing devices as described herein (and the algorithms, methods, instructions, etc., stored thereon and/or executed thereby) can be realized in hardware, software, or any combination thereof. The hardware can include, for example, computers, intellectual property (IP) cores, application-specific integrated circuits (ASICs), programmable logic arrays, optical processors, programmable logic controllers, microcode, microcontrollers, servers, microprocessors, digital signal processors or any other suitable circuit. In the claims, the term “processor” should be understood as encompassing any of the foregoing, either singly or in combination. The terms “signal” and “data” are used interchangeably. Further, portions of the computing devices do not necessarily have to be implemented in the same manner.

The aspects herein can be described in terms of functional block components and various processing operations. The disclosed processes and sequences may be performed alone or in any combination. Functional blocks can be realized by any number of hardware and/or software components that perform the specified functions. For example, the described aspects can employ various integrated circuit components, e.g., memory elements, processing elements, logic elements, look-up tables, and the like, which can carry out a variety of functions under the control of one or more microprocessors or other control devices. Similarly, where the elements of the described aspects are implemented using software programming or software elements the disclosure can be implemented with any programming or scripting language such as C, C++, Java, assembler, or the like, with the various algorithms being implemented with any combination of data structures, objects, processes, routines or other programming elements. Functional aspects can be implemented in algorithms that execute on one or more processors. Furthermore, the aspects of the disclosure could employ any number of conventional techniques for electronics configuration, signal processing and/or control, data processing and the like. The words “mechanism” and “element” are used broadly and are not limited to mechanical or physical implementations or aspects, but can include software routines in conjunction with processors, etc.

Implementations or portions of implementations of the above disclosure can take the form of a computer program product accessible from, for example, a computer-usable or computer-readable medium. A computer-usable or computer-readable medium can be any device that can, for example, tangibly contain, store, communicate, or transport a program or data structure for use by or in connection with any processor. The medium can be, for example, an electronic, magnetic, optical, electromagnetic, or a semiconductor device. Other suitable mediums are also available. Such computer-usable or computer-readable media can be referred to as non-transitory memory or media, and can include RAM or other volatile memory or storage devices that can change over time. A memory of an apparatus described herein, unless otherwise specified, does not have to be physically contained in the apparatus, but is one that can be accessed remotely by the apparatus, and does not have to be contiguous with other memory that might be physically contained in the apparatus.

Any of the individual or combined functions described herein as being performed as examples of the disclosure can be implemented using machine readable instructions in the form of code for operation of any or any combination of the aforementioned hardware. The computational codes can be implemented in the form of one or more modules by which individual or combined functions can be performed as a computational tool, the input and output data of each module being passed to/from one or more further module during operation of the methods and systems described herein.

Information, data, and signals can be represented using a variety of different technologies and techniques. For example, any data, instructions, commands, information, signals, bits, symbols, and chips referenced herein can be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, other items, or a combination of the foregoing.

The particular aspects shown and described herein are illustrative examples of the disclosure and are not intended to otherwise limit the scope of the disclosure in any way. For the sake of brevity, conventional electronics, control systems, software development and other functional aspects of the systems (and components of the individual operating components of the systems) may not be described in detail. Furthermore, the connecting lines, or connectors shown in the various figures presented are intended to represent exemplary functional relationships and/or physical or logical couplings between the various elements. Many alternative or additional functional relationships, physical connections or logical connections may be present in a practical device.

The word “example” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “example” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word “example” is intended to present concepts in a concrete fashion. As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X includes A or B” is intended to mean any of the natural inclusive permutations. In other words, if X includes A; X includes B; or X includes both A and B, then “X includes A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form. Moreover, use of the term “an aspect” or “one aspect” throughout is not intended to mean the same implementation or aspect unless described as such.

The use of “including” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” ‘supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.

The use of the terms “a” and “an” and “the” and similar referents in the context of describing the disclosure (especially in the context of the following claims) should be construed to cover both the singular and the plural. Furthermore, recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. Finally, the steps of all methods described herein are performable in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the disclosure and does not pose a limitation on the scope of the disclosure unless otherwise claimed.

This specification has been set forth with various headings and subheadings. These are included to enhance readability and ease the process of finding and referencing material in the specification. These heading and subheadings are not intended, and should not be used, to affect the interpretation of the claims or limit claim scope in any way. The particular implementations shown and described herein are illustrative examples of the disclosure and are not intended to otherwise limit the scope of the disclosure in any way.

All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated as incorporated by reference and were set forth in its entirety herein.

While the disclosure has been described in connection with certain embodiments and implementations, it is to be understood that the disclosure is not to be limited to the disclosed implementations but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law. 

What is claimed is:
 1. A method for encoding a video stream, comprising: encoding, by a processor, a first slice of a first picture of the video stream; receiving, from a decoder, a feedback message indicative of having received the first slice of the first picture; and in response to receiving the feedback message indicative of having received the first slice of the first picture, setting the first slice of the first picture as a reference slice for encoding a second picture of the video stream, wherein the second picture is encoded after receiving the feedback message.
 2. The method of claim 1, further comprising: encoding, by the processor, a first slice of the second picture of the video stream with reference to the first slice of the first picture, wherein the first slice of the first picture and the first slice of the second picture are co-located.
 3. The method of claim 2, wherein encoding, by the processor, the first slice of the second picture of the video stream with reference to the first slice of the first picture further comprises: encoding a slice header of the first slice of the second picture with reference to the first slice of the first picture, wherein the first slice of the first picture is used for predicting the first slice of the second picture during decoding.
 4. The method of claim 1, further comprising: based on a determination that the first picture has not been set as a reference picture and in response to receiving the feedback message indicative of having received the first slice of the first picture, setting the first picture as a new reference picture for encoding the second picture of the video stream.
 5. The method of claim 4, wherein the first picture is set as a new long-term reference (LTR) picture, and the first slice of the first picture is set as a valid reference slice.
 6. The method of claim 5, further comprising: receiving, from the decoder, a second feedback message indicative of having received a second slice of the first picture, wherein the second slice of the first picture is not the same as the first slice of the first picture; and in response to receiving the second feedback message, setting the second slice of the first picture as a reference slice for encoding the second picture of the video stream, wherein both the first slice and the second slice of the first picture are set as valid reference slices.
 7. The method of claim 5, further comprising: in response to setting the first slice of the first picture as the reference slice for encoding the second picture of the video stream, setting a first slice of a third picture of the video stream as an invalid reference slice, wherein the first slice of the first picture and the first slice of the third picture are co-located, the third picture encoded prior to encoding the first picture.
 8. The method of claim 5, wherein a set of reference pictures used for predicting the second picture comprises each picture associated with at least one valid reference slice.
 9. The method of claim 8, wherein the set of reference pictures used for predicting the second picture further comprises a fourth picture encoded immediately prior to encoding the second picture.
 10. The method of claim 1, wherein the feedback message indicative of having received the first slice of the first picture is indicative of having received the first slice and at least one other slice of the first picture.
 11. A method for decoding an encoded video stream, comprising: receiving, from an encoder, data associated with a first slice of a first picture of the encoded video stream; based on a determination that all data required for decoding the first slice of the first picture has been received, sending, to the encoder, a feedback message indicative of having received the first slice of the first picture, and decoding, by a processor, the first slice of the first picture; receiving, from the encoder, data associated with a first slice of a second picture of the encoded video stream with reference to the first slice of the first picture; and setting the first slice of the first picture as a reference slice for decoding the second picture of the encoded video stream.
 12. The method of claim 11, further comprises: decoding, by the processor, the first slice of the second picture of the encoded video stream with reference to the first slice of the first picture, wherein the first slice of the first picture and the first slice of the second picture are co-located.
 13. The method of claim 12, wherein decoding, by the processor, the first slice of the second picture of the encoded video stream with reference to the first slice of the first picture further comprises: decoding a slice header of the first slice of the second picture with reference to the first slice of the first picture, wherein the first slice of the first picture is used for predicting the first slice of the second picture during decoding.
 14. The method of claim 11, further comprising: based on a determination that the first picture has not been set as a reference picture and in response to receiving, from the encoder, data associated with the first slice of the second picture with reference to the first slice of the first picture, setting the first picture as a new reference picture for decoding the second picture of the encoded video stream.
 15. The method of claim 14, wherein the first picture is set as a new long-term reference (LTR) picture, and the first slice of the first picture is set as a valid reference slice.
 16. The method of claim 15, further comprising: based on a determination that all data required for decoding a second slice of the first picture has been received, sending, to the encoder, a second feedback message indicative of having received the second slice of the first picture, and decoding, by a processor, the second slice of the first picture, wherein the second slice of the first picture is not the same as the first slice of the first picture; and receiving, from the encoder, data associated with a second slice of the second picture of the encoded video stream with reference to the second slice of the first picture; and setting the second slice of the first picture as a reference slice for decoding the second picture of the encoded video stream, wherein both the first slice and the second slice of the first picture are set as valid reference slices.
 17. The method of claim 15, further comprising: in response to setting the first slice of the first picture as the reference slice for decoding the second picture of the encoded video stream, setting a first slice of a third picture of the encoded video stream as an invalid reference slice, wherein the first slice of the first picture and the first slice of the third picture are co-located, the third picture decoded prior to decoding the first picture.
 18. The method of claim 15, wherein a set of reference pictures used for predicting the second picture comprises each picture associated with at least one valid reference slice and a fourth picture decoded immediately prior to decoding the second picture.
 19. The method of claim 11, wherein the feedback message indicative of having received the first slice of the first picture is indicative of having received the first slice and at least one other slice of the first picture.
 20. An apparatus for decoding an encoded video stream, comprising: a non-transitory memory; and a processor, wherein the non-transitory memory includes instructions executable by the processor to: receive, from an encoder, data associated with a first slice of a first picture of the encoded video stream; based on a determination that all data required for decoding the first slice of the first picture has been received, send, to the encoder, a feedback message indicative of having received the first slice of the first picture, and decode, by a processor, the first slice of the first picture; and receive, from the encoder, data associated with a first slice of a second picture of the encoded video stream with reference to the first slice of the first picture; and set the first slice of the first picture as a reference slice for decoding the second picture of the encoded video stream. 